It is often necessary to determine revolutions per unit time of an internal combustion engine. Such a measurement typically uses a device known as a tachometer. Tachometers are most often used in automotive applications. For instance, applications for repetitive automotive testing may require an accurate RPM reading. This is required in such fields as automotive emission testing or safety inspections. Such testing operations not only require an accurate measurement of RPM, but also require that the device be easily and temporarily attached to the automobile operative portions. Much time can be saved if the user does not have to physically connect the device to the internal combustion engine.
Devices in the prior art have typically either physically connected a device to a moving part of the internal combustion engine, or have used an optical sensor to detect the movement of the internal combustion engine. The use of an optical sensor is disadvantageous since a white line or marker of that type must be attached to the internal combustion engine before the detection can be made. Moreover, this white line can become obscured by natural grease that forms within the engine compartment of the engines.
Physical contact with the internal combustion engine can also be dangerous for the people operating the device.
Furthermore, many new engines being manufactured today use a so-called distributorless system. These engines will not accommodate a conventional tachometer system. For instance, the GM Quad 4 has no accessible spark plug wires or exposed ignition cords. The inventors of the present invention have found that a non-contact antenna system which senses electromagnetic signals produced by firing of the engine, would lend itself very well to this application. Such a system could be used with no specialized testing equipment being required, nor would any complicated hook-ups be necessary.
It would also be advantageous if this tachometer system could interface with a personal computer. This would enable RPM readings to be stored in the computer's memory and to perform comparative analysis of RPM versus hydrocarbon, carbon monoxide or carbon dioxide emissions.